Sometimes I want to be a healer/support character, sometimes operate MM like a marionette/puppet, sometimes shoot a rifle from a distance, sometimes be a Brute SMASH! sometimes a stealthy ninja.
Sometimes be an adventurer, sometimes a strong yet beautiful lady (think DC's Knockout), sometimes a cat, sometimes robot.
Fly, Run, Teleport....
Fire, Ice, Dark...
Nearly unlimited variety and customization depending on the current mood and/or trend as opposed to playing generic warrior #2.